1. Field of the Invention
The present invention relates to an inking mechanism in a rotary press, more particularly, an ink scraper device for a mesh roll in a rotary press wherein a two-roll system for flexographic printing, i.e. a system for transferring the ink in an ink pan to an Anilox roll (having another name of mesh roll or screened roll) via a fountain roll is utilized, comprising a doctor blade adapted to be brought into contact at a free end portion thereof with the circumferential surface of the mesh roll to scrape off excess ink therefrom.
2. Description of the Prior Art
It has recently been demonstrated that a printing mechanism for a newspaper rotary press can be simplified, miniaturized and reduced in weight and manufacturing cost by making use of the advantage of flexographic printing technique wherein a single mesh roll is used to omit using a plurality of ink cylinders.
It is necessary that a newspaper rotary press be rotated at a very high speed in order to inform people of daily events early. When, for example, 70,000 copies of newspaper are printed per hour, a web runs through each part of a printing mechanism at 35-40 km/hr.
A fountain roll for use in drawing ink from an ink pan is operated properly even when the rotational speed is reduced to 1/20 of the peripheral speed of a plate cylinder, i.e. not more than around 2 km/hr. Therefore, the scattering of ink mist can substantially be prevented. Namely, rotating a fountain roll at a low speed causes no trouble.
On the other hand, it is necessary that the mesh roll, to which ink is transferred from the fountain roll, be adapted to constantly feed ink film onto the plate cylinder. In other words, it is necessary that the mesh roll be rotated at the same peripheral speed as the plate cylinder. When the feed rate of ink onto the circumferential surface of the mesh roll is even a little too high, ink mist is scattered by a great centrifugal force.
The scattering of ink mist at the circumferential surface of the mesh roll may be surely prevented if any excess ink is scraped off therefrom the moment the ink is transferred from the fountain roll onto the circumferential surface of the mesh roll.
In order to attain the removal of excess ink from the circumferential surface of the mesh roll, it is necessary to dispose a doctor blade such that a free end portion of the doctor blade is projected toward the contact point of the fountain roll and mesh roll so as to be brought into contact, in opposition to the rotational direction of the mesh roll (at a reverse angle), with that portion of the circumferential surface of the mesh roll which is immediately after the position where ink is transferred.
However, when the doctor blade is stationarily extended in an extremely narrow gap between the two rolls referred to above, the inspection, cleaning and replacement of the blade cannot be carried out speedily and sufficiently with ease. Under such circumstances, a prompt printing of newspapers cannot possibly be attained. In fact, the inspection, cleaning and replacement of a doctor blade have to be carried out in quick and accurate steps as in the case of the replacement of a tire of a/pitted-in racing car. This makes it necessary to develop a displacement means which permits displacing at a large angle the doctor blade from such a narrow space as mentioned above to a place where it can be easily inspected, cleaned and replaced.
However, a doctor blade which is capable of being displaced at a large angle may not be practically useful unless the excess ink, which has been scraped off by the doctor blade, always returns by way of the shortest distance into the ink pan along the circumferential surface of the fountain roll without causing scattering of ink mist.
If the ink is a viscous liquid and has turbulent flow it will contain many air bubbles which have great difficulty leaving the ink.
The bubbles are transferred to the mesh roll via the fountain roll from the ink pan, and the bubbles will enter the reticulate grooves of the mesh roll which prevents the ink attaching in the reticulate grooves of the mesh roll. Consequently, smooth printing is prevented due to the bubbles and the quality of printing drops.
On the other hand, since the bubbles mixed in the ink are broken at the closing position between the rolls contacting each other, the bubble bursts cause the scattering of ink mist and makes the printing paper dirty.